1. Field of the invention
The present invention relates to a superconducting coil and a method for producing the same, more particularly it relates to a superconducting coil composed of a compound oxide type superconducting material.
The coil according to the present invention is applicable for manufacturing a small and light-weight actuator, motor or generator, electromagnetic valve, sensor or the like.
2. Description of the related art
A superconducting coil or solenoid which is realized by metal type superconductor such as a Ti-Nb alloy is already known and has been developed for a superconducting magnet or the like.
The critical temperature (Tc) of the metal type superconductors, however, could not exceed 23.2K of Nb.sub.3 Ge which was the highest Tc for all studies for the past ten years and hence the use of liquidized helium (boiling point of 4.2K) as cryogen is indispensable for superconductivity. Therefore, their actual application is limited to special industrial or scientific fields and it is difficult to reduce their size or diameter to less than several 10 mm at present.
The possibility of the existence of a new type of superconducting material having a much higher Tc was revealed by Bednorz and Muller who discovered a new oxide type superconductor in 1986 [Z. Phys. B64 (1986) 189]. This new oxide type superconducting material discovered by Bednorz and Muller is [La, Ba].sub.2 CuO.sub.4 which is called the K.sub.2 NiF.sub.4 -type oxide having a crystal structure which is similar to the known perovskite type oxide. The K.sub.2 NiF.sub.4 -type oxides show such a high Tc as 30K which is extremely higher than the known superconducting materials. It was also reported in the news paper that C. W. Chu et al. discovered in the United States of America another type of superconducting material having the critical temperature of about 90K in Feb. 1987. This superconductor called as YBCO is a compound oxide of Ba-Y system represented by YBa.sub.2 Cu.sub.3 O.sub.7 -.delta..
From the discovery of the abovementioned new type of compound oxide type superconductors, the existence of high-temperature superconductors which exhibit superconductivity in inexpensive and readily available liquid nitrogen have arisen suddenly.
However, the abovementioned compound oxide is a ceramic material so that it is difficult or impossible to directly adopt the conventional techniques which are used in the metal type superconductors for producing a solenoid or coil.
Therefore, an object of the present invention is to provide a superconducting coil consisting of new type compound oxide which possesses a high critical temperature (Tc) and a method for producing the same.